Screen magnifiers are a type of assistive technology used by visually impaired people with some functional vision. By magnifying areas of the screen, the screen magnifier allows people that would otherwise not be able to see areas of the screen that are too small to enlarge these areas. Screen magnifiers are software applications that present a computer's graphical output in an enlarged form. Many screen magnifiers act similar to a physical magnifying glass that a user can move around over the screen to magnify a specific area, except rather than a physical object the screen magnifier is software and the user moves the displayed glass or lens with the mouse or other input device. The most common method of magnification is to present an enlarged view of a portion of the original screen content that covers a portion of or the entire screen. The enlarged view often tracks the pointer or cursor as the user moves a mouse or other input device around the screen so that the user can magnify different areas. Screen magnifiers may work with a single application or across multiple applications at the operating system level. For example, Microsoft Windows Vista includes Magnifier, an application for magnifying the entire desktop and any applications displayed on it.
Because the view is enlarged, screen magnifiers provide a way to move the lens, or magnified area, to different areas of the desktop or application. For example, at a magnification factor of 4 times (4×), only one-eighth of the desktop can be shown in a full screen magnifier at a time. Thus, to see the other three-fourths of the desktop a user moves the magnified area around in a process called panning. Although panning often refers only to horizontal movement (and scrolling or other terms refer to vertical movement), panning and movement as used herein refer to movement of the magnified view in any direction, whether horizontally, vertically, or diagonally.
A tablet PC, or pen computer, is a notebook or slate-shaped mobile computer, equipped with a touch screen or graphics tablet/screen hybrid technology that allows the user to operate the computer with a stylus, digital pen, or fingertip instead of a keyboard or mouse. Tablet PCs offer a more natural form of input, as sketching and handwriting are a much more familiar form of input than a keyboard and mouse, especially for people who are new to computers. Tablet PCs can also be more accessible because those who are physically unable to type can utilize the additional features of a tablet PC to be able to interact with the electronic world. Applications often do not know they are running on a tablet PC, and the operating system may attempt to provide input to applications that appears similar to mouse input. This can cause several problems for screen magnifiers used in conjunction with tablet PCs or other touch-based interface devices.
One problem is that most screen magnifiers do not handle touch or other natural input in any special way. For example, the screen magnifier may receive notifications from the operating system about natural input operations that are similar to mouse input (e.g., click, hover, move left). This means that at best, the natural input functions on par with previous forms of input with the screen magnifier, and possibly introduces new and awkward difficulties with interacting with the screen magnifier. For example, unlike a mouse touch-based interface devices may not distinguish between setting the pen down to move it (e.g., panning a magnification area) and tapping the screen to click an object (e.g., selecting an icon).
To resolve this ambiguity, some applications have an exclusive panning mode (e.g., often represented by a hand icon) that informs the application to interpret movements of the pen or other device as panning movements, when selected. In this mode, the application locks the display area to the cursor position and moves the display area as the user moves the cursor to perform panning. However, this type of panning mode prevents the user from performing activities other than panning, such as clicking on or interacting with user interface elements, until the user leaves the exclusive panning mode. In addition, applications that are magnified often are designed to provide special benefits to touch-based users, such as pen gestures that the user can make to perform special functions. It is ambiguous when a user makes one of these gestures in the screen magnifier whether the user is intending to interact with the application or the screen magnifier.